[llvm-dev] FYI: Ninja-build user may use CMake-3.9

Reid Kleckner via llvm-dev llvm-dev at lists.llvm.org
Thu Jul 20 09:16:49 PDT 2017

This is great news! Do we know who contributed the changes to cut the extra
library dependencies?

Do you think we should remove ENABLE_OBJLIB to simplify our CMake files in
the near future? It seems to me that anyone who cares about highly parallel
build throughput can upgrade CMake to get the good behavior. It's probably
easier and less error-prone than maintaining a special build configuration.

On Thu, Jul 20, 2017 at 8:31 AM, NAKAMURA Takumi via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> This is useful for developer who uses multicore builder.
> https://cmake.org/cmake/help/v3.9/release/3.9.html#other-changes
>    - The Ninja
>    <https://cmake.org/cmake/help/v3.9/generator/Ninja.html#generator:Ninja> generator
>    has loosened the dependencies of object compilation. Object compilation now
>    depends only on custom targets and custom commands associated with
>    libraries on which the object’s target depends and no longer depends on the
>    libraries themselves. Source files in dependent targets may now compile
>    without waiting for their targets’ dependencies to link.
> With BUILD_SHARED_LIBS, compiling units don't wait for preceding shared
> libs.
> See also; http://bb.pgr.jp/builders/i686-mingw32-RA-on-linux
> Regardless of BUILD_SHARED_LIBS, compile units in add_executable() don't
> wait for preceding libraries,
> but targets by add_dependencies().
> It doesn't break anything in llvm tree. Assume;
>   add_executable(foo foo.cpp)
>   target_link_libraries(foo LLVMCore) # depends on intrinsics_gen
> Compiling foo.cpp doesn't wait for LLVMCore, but intrinsics_gen.
> Linking foo waits for LLVMCore.
> I have been working for cutting dependencies to increase parallelism.
> For example, I introduced ENABLE_OBJLIB.
> See also, https://reviews.llvm.org/rL305635
> Ninja with CMake-3.9 doesn't require parallelize with objlib.
> I love ninja-build.
> Thanks,
> Takumi
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